Readme.txt vs. README.txt (2015)

READ.ME just looks cool, same thing as with internet domains.

Edit: I even remember seeing this somewhere as a child and admiring how clever it was (Commander Keen maybe?).

And the capitalization thing in this case is of course also a DOS thing (as opposed to the newer traditions pointed out by another comment.

Tangent: on DOS and Windows, filenames without a file extension suffix were just weird. I mostly expected them to contain binary data :D

Say, you're connecting to BBS with A LOT of files. Unless you already know that "SEX459W.ZIP" and "SEX454.ZIP" are Windows and DOS versions of (fictitious) “Super Extractor 4.5”, you'll spend a lot of time figuring it out. People who pay no attention to file categories can also get intrigued without a cause. Therefore, full names and descriptions were stored in sidecar files, and were processed to form complete file listings (to download and study offline). Sometimes operators personally reviewed the software, adding interesting opinions about users who had it on their computers, sometimes those were simple excerpts from release notes.

In some cases, the metadata was automatically appended to archives (as standard comments). Later, in the era of Rich Formats, WinZip even allowed arbitrary HTML in ZIP comments, and automatically loaded them into IE frame instead of regular text box when opening such archive. Obviously, that novelty didn't last long.

https://developer.ibm.com/tutorials/l-linux-shells/

Early on it used esc instead of tab.

I also found in the bash changelog from 1996 there are fixes to crashing bugs in file name completion.

However, I stand by what I said. It was common for people not to know about filename completion. It was common to ship without it by default. Most clued in people installed bash on those systems. But not everybody.